for National Geographic News
The freeze-thaw, freeze-thaw see-saw of this winter's temperatures may be a sign of global warming. But for now wood frogs are weathering the flux in style, according to an expert on the amphibians.
"They undergo freeze-thaw cycles all the time," said Kenneth Storey, a professor of biochemistry at Carleton University in Ottawa, Canada.
Some animals migrate to warmer climes for the winter and others burrow deep underground to sleep until spring. Wood frogs instead seek cover under leaves near the surface, where they actually freeze and thaw with their surroundings.
In his lab, Storey has taken the frogs through multiple consecutive freeze-thaw cycles and found no adverse effects. In nature the frogs consistently go through freeze-thaw cycles, he said.
"We have false springs here all the time where it gets really warm and all the snow melts and then suddenly—bam—the wind comes from the north and it's back down to minus 10, minus 15 [degrees Celsius], and they're fine," he said.
"So in nature and in the lab they have to do it, and they do."
Storey studies the molecular mechanics that allow wood frogs to freeze and thaw. He hopes that doctors will one day be able to copy the technique to aid human organ transplants.
Currently doctors only have hours to get a donated organ into a living patient before the organ becomes too damaged. Freezing organs isn't an option, as the cells dehydrate.
Once the first ice crystals reach a wood frog, however, its skin freezes. The frog becomes hard and crunchy. "When you drop it, it goes 'clink,'" Storey said.
Special proteins in their blood, called nucleating proteins, cause the water in the blood to freeze first. This ice, in turn, sucks most of the water out of the frog's cells.
At the same time the frog's liver starts making large amounts of glucose—a type of sugar—which packs into cells and props them up.
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